You can see the error here, and my fix. In the launcher, I set it to

name=h5

descr="load waves"

tclcommand="simuldir; xschem raw_read $netlist_dir/tb_nfet.raw dc"

i.e. calling simuldir first. This was enough to get everything setup. Might be a better way. This is with v3.4.4 as running in the tinytapeout VM.